The present invention relates to an ink-jet recording head using a piezoelectric thin film as a driving source for ink discharge, an ink-jet recording apparatus provided with this ink-jet recording head, such as an ink-jet printer used as an output equipment of a personal computer, a facsimile or a word processor, and a method for producing an ink-jet recording head. More particularly, it relates to an improvement in an electrode forming technique.
There is a piezoelectric type ink-jet recording head using piezoelectric elements formed of lead zirconate titanate as electromechanical transducer elements, driving sources for liquid or ink discharge. This recording head generally comprises a head base on which a large number of separate ink passages are formed, a diaphragm attached to the head base so as to cover all of the separate ink passages, and piezoelectric elements deposited onto respective parts on the diaphragm corresponding to the separate ink passages. An electric field is applied to the piezoelectric element to displace it, thereby pushing out ink existing in the separate ink passage through a nozzle of the separate ink passage.
As one example, International Patent Application Laid-open In Japan No. Hei. 5-504740 is present. Then, a method for producing an ink-jet recording head described in this publication will be illustrated with reference to the drawings.
As shown in FIG. 35, a silicon oxide film SID is formed on a silicon substrate SI, and a conductive layer FMF formed of a platinum, aluminum or nickel thin film as a lower electrode is formed thereon. Then, as shown in FIG. 36, a resist area DRS exposed to light photolithography is formed on the conductive layer, and as shown in FIG. 37, an electrode pattern FML is formed by using this resist area DRS exposed to light as a mask.
Next, as shown in FIG. 38, lead zirconate titanate PEZ which is a kind of piezoelectric thin film is further formed by the sol-gel method, and subsequently, a second metal thin film SMF as an upper electrode is deposited so as to cover lead zirconate titanate PEZ. Further, a resist RS is formed so as to cover the second metal thin film SMF.
Then, a resist area DRS exposed to light is formed so that a second electrode pattern is obtained by irradiating ultraviolet light rays through a mask MSK.
Further, as shown in FIG. 39, after formation of the second electrode pattern SML, a protective film PSV is deposited onto it. Furthermore, as shown in FIG. 39, a resist is deposited onto a second main surface of the silicon substrate, and then as shown in FIG. 40, ultraviolet light rays are irradiated through a mask MSK to form a resist area DRS exposed to light.
Then, as shown in FIG. 41, the resist is separated so as to leave the resist area DRS exposed to light, and the silicon substrate SI is subjected to anisotropic etching in a strong alkaline solution. The resist area DRS exposed to light is further separated to form ink cavity chambers CAV.
However, in the method for producing the ink-jet recording head described above, no consideration is given to formation of the first and second electrode patterns FML and SML, and the ink cavity chambers CAV at an exact position without deviation from each other. Then, in order to form the electrode patterns and the ink cavity chambers at an exactly adjusted position, photolithography with a both side exposure device is applied to the method described above.
However, patterning of the electrode of the ink-jet recording head by the photolithography method introduce the problem that the electrode is electrolytically corroded with the developing solution used when the resist exposed to light is developed, resulting in failure to form the electrode pattern.
That is, when the first electrode pattern is made of platinum and the second electrode pattern is made of a material different therefrom, and when a positive resist for photolithography is selected from the viewpoints of low cost and improved patterning accuracy for patterning of the electrode and protection of the electrode, the electrolytic corrosion phenomenon occurs between platinum and the second metal thin film due to the difference in electrochemical potential, because the developing solution for the positive resist is an alkaline electrolytic solution.
For example, when the first electrode pattern LE is platinum and the second electrode pattern is aluminum, the phenomenon occurs that hydrogen gas is produced from platinum of the first electrode to dissolve or separate aluminum of the second electrode. This electrolytic corrosion phenomenon introduces the problems that poor formation of the electrode pattern takes place in the ink-jet recording head, and further, that no piezoelectric element can be formed.
It is therefore an object of the present invention to provide an ink-jet recording head not having poor formation of an electrode pattern caused by such an electrolytic corrosion phenomenon, and an ink-jet recording apparatus provided with the same. Further, another object of the present invention is to provide a method by which it can be produced without generation of the above-mentioned electrolytic corrosion phenomenon.
On the other hand, in order to discharge a large amount of ink from a ink-jet head, it is desirable that a diaphragm is largely displaced. For this purpose, for example, a platinum thin plate having a higher Young's modulus is used as the first metal thin film, and a metal thin film having a lower Young's modulus is used as the second metal thin film. An aluminum thin film has a very low Young's modulus. Accordingly, when a voltage is applied to a piezoelectric element device, it is displaced twice or more compared with the case that the first and second metal thin films are both made of platinum.
However, when the electrochemical potential of the second metal thin film is base to that of the first metal thin film, there is the problem that the above-mentioned electrolytic corrosion phenomenon takes place in patterning the second metal thin film by photolithography, resulting in failure to obtain a good pattern of the second metal thin film.